/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.jasper.compiler.tagplugin;

/**
 * This interface allows the plugin author to make inqueries about the
 * properties of the current tag, and to use Jasper resources to generate direct
 * Java codes in place of tag handler invocations.
 */

public interface TagPluginContext {
	/**
	 * @return true if the body of the tag is scriptless.
	 */
	boolean isScriptless();

	/**
	 * @param attribute
	 *            Name of the attribute
	 * @return true if the attribute is specified in the tag
	 */
	boolean isAttributeSpecified(String attribute);

	/**
	 * @return An unique temporary variable name that the plugin can use.
	 */
	String getTemporaryVariableName();

	/**
	 * Generate an import statement
	 * 
	 * @param s
	 *            Name of the import class, '*' allowed.
	 */
	void generateImport(String s);

	/**
	 * Generate a declaration in the of the generated class. This can be used to
	 * declare an innter class, a method, or a class variable.
	 * 
	 * @param id
	 *            An unique ID identifying the declaration. It is not part of
	 *            the declaration, and is used to ensure that the declaration
	 *            will only appear once. If this method is invoked with the same
	 *            id more than once in the translation unit, only the first
	 *            declaration will be taken.
	 * @param text
	 *            The text of the declaration.
	 **/
	void generateDeclaration(String id, String text);

	/**
	 * Generate Java source codes
	 */
	void generateJavaSource(String s);

	/**
	 * @return true if the attribute is specified and its value is a
	 *         translation-time constant.
	 */
	boolean isConstantAttribute(String attribute);

	/**
	 * @return A string that is the value of a constant attribute. Undefined if
	 *         the attribute is not a (translation-time) constant. null if the
	 *         attribute is not specified.
	 */
	String getConstantAttribute(String attribute);

	/**
	 * Generate codesto evaluate value of a attribute in the custom tag The
	 * codes is a Java expression. NOTE: Currently cannot handle attributes that
	 * are fragments.
	 * 
	 * @param attribute
	 *            The specified attribute
	 */
	void generateAttribute(String attribute);

	/**
	 * Generate codes for the body of the custom tag
	 */
	void generateBody();

	/**
	 * Abandon optimization for this tag handler, and instruct Jasper to
	 * generate the tag handler calls, as usual. Should be invoked if errors are
	 * detected, or when the tag body is deemed too compilicated for
	 * optimization.
	 */
	void dontUseTagPlugin();

	/**
	 * Get the PluginContext for the parent of this custom tag. NOTE: The
	 * operations available for PluginContext so obtained is limited to
	 * getPluginAttribute and setPluginAttribute, and queries (e.g.
	 * isScriptless(). There should be no calls to generate*().
	 * 
	 * @return The pluginContext for the parent node. null if the parent is not
	 *         a custom tag, or if the pluginConxt if not available (because
	 *         useTagPlugin is false, e.g).
	 */
	TagPluginContext getParentContext();

	/**
	 * Associate the attribute with a value in the current tagplugin context.
	 * The plugin attributes can be used for communication among tags that must
	 * work together as a group. See <c:when> for an example.
	 */
	void setPluginAttribute(String attr, Object value);

	/**
	 * Get the value of an attribute in the current tagplugin context.
	 */
	Object getPluginAttribute(String attr);
}
